Hydrostatic steering device

Abstract

A hydrostatic steering device is provided with a pump connected with a reservoir, a steering valve, a controlled-volume pump that is capable of being activated by a steering wheel and with a steering cylinder. The steering mechanism has a variable working flow and a constant pilot flow, with the pilot stream flowing through a constant throttle and the pressure drop through the constant throttle serving as a control signal for the conveying flow in a pressure delivery line. The controlled-volume pump is coupled mechanically with an adjustment throttle through which the pilot flows. Between the constant throttle and the adjustment throttle lies a pressure compensator that is controlled by the adjustment throttle's differential pressure. To receive the load signal, a control line branches off between the constant throttle and the pressure compensator and leads to the pump or, in the case of a fixed displacement pump with a rear-position flow-dividing valve, to the flow-dividing valve.

I claim: 
     
       1. In a hydrostatic steering device including a pump (2) connected with a reservoir (1), a steering valve (4) connected with said pump via a variable pressure line (3) and a constant pilot line (5), a controlled-volume pump (8) activated by a steering wheel and connected with said steering valve, a steering cylinder (13) connected with said steering valve, a constant throttle connected with said pilot line to produce a pressure drop which serves as a control signal for the flow in said variable pressure line, an adjustment throttle (15) connected with said pilot line and arranged in said steering valve for connection with said controlled-volume pump, the improvement which comprises (a) a pressure compensator (16) connected with said pilot line between said constant and adjustment throttles, said compensator being controlled by a differential pressure of said adjustment throttle; and   (b) a control line (18) connected with said pilot line between said constant throttle and said compensator and with said pump for delivering said control signal to said pump.   
     
     
       2. A hydrostatic steering device as defined in claim 1, wherein said pressure compensator includes a spring (17) which biases one face of said compensator, the other face of said compensator being biased by the pressure from said adjustment throttle. 
     
     
       3. A hydrostatic steering device as defined in claim 1, wherein said adjustment throttle has a characteristic curve which is linear with the excursion angle of the steering wheel. 
     
     
       4. A hydrostatic steering device as defined in claim 2, wherein said adjustment throttle contains an opening affording communication of hydraulic fluid between a housing and a plunger of said steering valve. 
     
     
       5. A hydrostatic steering device as defined in claim 3, wherein said pressure compensator contains an adjustment plunger (25) having a control bevel (30). 
     
     
       6. A hydrostatic steering device as defined in claim 2, wherein said spring is a weak spring, whereby the differential pressure controlling said pressure compensator is kept low. 
     
     
       7. A hydrostatic steering device as defined in claim 1, wherein said pump comprises a fixed displacement pump, and further comprising a flow-divider valve (21) connected with said pump for dividing said hydraulic fluid between two circuits (I, II), said control line being connected with said flow-divider valve to control the pressure in each circuit.